An example of methods for producing bioethanol using cellulose-based biomass as a raw material is an enzymatic ethanol production technique of producing a solution (hereafter referred to as a “saccharified solution”) containing a saccharide containing glucose as a main component by enzymatically hydrolyzing at least one of cellulose and hemicellulose contained in cellulose-based biomass.
One of difficulties for putting the enzymatic ethanol production technique into practical use is to decrease the amount of an enzyme used. To decrease the amount of an enzyme used, the contact efficiency between the enzyme and at least one of cellulose and hemicellulose needs to be increased by performing a pretreatment for breaking the structure of biomass.
In the pretreatment for biomass, for example, water vapor, an acid, or an alkali is added to the biomass and heat and pressure are applied thereto. As a result of this pretreatment, lignin, cellulose, and hemicellulose in the biomass are degraded to produce organic acids and tars. These products (hereafter, may be referred to as “inhibitors”) are generally known to inhibit an enzymatic saccharification reaction and a fermentation reaction in which saccharides obtained from biomass are converted into ethanol (e.g., refer to NPL 1).
Therefore, organic acids and the like are desirably removed by washing the biomass that has been subjected to a pretreatment in order to efficiently cause an enzymatic saccharification reaction.